Preparation Of Poly(Vinyl Acetate) And Its Composite With Carbon Nanotubes And Carbon Black Through Emulsion Polymerization Under Ultrasonic Irradiation

In this study, ultrasonic irradiation was introduced to emulsion polymerization of vinyl acetate and preparation of composites with some inorganic nanoparticles. Some novel materials with special structure and properties were prepared. The main conclusions are as follows:Taking advantages of ultrasound, i.e. its pulverization, dispersion, activation, and initiation, emulsion polymerization of vinyl acetate at low temperature was realized and the affecting factors were studied. The results showed that the conversion of monomer could reach～60% within 60min at 25℃under the appropriate reaction conditions of 7 mL monomer VAc, 63 ml H₂O, 1wt% SDS, 1mM KPS and power output 900W. The realization of VAc polymerization at low temperature was contributed to the cavitation effect. Under ultrasonic irradiation, the decomposition of potassium persulfate and SDS could proceed quite fast at low temperature, which would produce large amount of radicals to get higher monomer conversion in shorter time and at lower reaction temperature. It was validated that there were only two phases, including acceleration and deceleration one, but no constant-rate phase occurring in the emulsion polymerization process of VAc. The structure of PVAc obtained by emulsion polymerization of VAc under ultrasonic irradiation was characterized by viscometry, GPC, FTIR and TEM. The experimental results showed that the average particle size of PVAc latex particles was at nano scale. Compared with PVAc obtained by conventional emulsion polymerization, the one prepared by ultrasonic irradiation had higher molecular weight, narrower molecular weight distribution and higher tacticity.Based on the emulsion polymerization of VAc under ultrasonic irradiation, polymeric composites with higher conductivity were obtained by utilizing"bridging effect" of CNTs with high aspect ratio. The whole procedure contained two steps. First, ultrasonic irradiation was employed to prepare PVAc/CNTs latex by emulsion polymerization of VAc in the presence of CNTs, which was served as seed latex to conduct the subsequently conventional emulsion polymerization for the purpose of enhancing solid content. Second, the well-dispersed carbon black in solution was mixed with the above emulsion to prepare PVAc/CNTs/carbon black composites. The dispersion behavior of CNTs in the emulsion was investigated by spectrophotometry and TEM. The results suggested that ultrasonic irradiation was a more effective way to break down the aggregates and entanglement of CNTs and realize their uniform dispersion as compared with conventional stirring method. Resistivity measurement showed that addition of CNTs increased the conductivity of the composite because carbon blacks were connected together by CNTs, forming conductive networks, which was proved by TEM observation.